A known problem with bicycle hydraulic disc brake master cylinders stems their evolution from motorcycle hydraulic disc brake master cylinder levers. Known bicycle hydraulic disc brake levers are generally scaled down motorcycle levers. Motorcycle levers are intended for use by all four fingers of a user. Accordingly, loses in mechanical advantage as a motorcycle lever is actuated is of little concern because of the amount of force the whole hand of a user can apply.
Heretofore, the manufactures of hydraulic brake levers for bicycles failed to recognize that motorcycle lever geometry is not favorable. The reason the motorcycle levers tend to result in a loss of mechanical advantage as the lever is applied is primarily because the pivot point of the lever is located relatively far away from an axis of a clamp securing the lever to the motorcycle handlebar. Known prior art bicycle hydraulic disc levers incorporate this unfavorable geometry. For example, a Brand A lever is known to make a hydraulic disc lever having the lever pivot axis the closest to the clamp axis. The Brand A lever has the pivot axis 50 mm from the clamp axis. However, observation of user ergonomics indicates that the engagement point of the lever (the point where pads on an associated caliper contact the disc) should be less than 50 mm to accommodate average and smaller sized hands. The geometry further fails to recognize that users' fingers will almost always travel in an actuation path of 90° or more from the clamp axis. As a result, a pivot spacing of 50 mm results in a decreasing mechanical advantage with finger travel being at an angle of 90° or more. Thus, there is a need to provide a lever having an engagement point 50 mm or less from the clamp axis and a pivot spacing less than the engagement point spacing so as to provide an increasing mechanical advantage over at least a portion of the lever actuation stroke.
It should be further noted that the lever geometry with the pivot point 50 mm or greater from the clamp axis cannot readily be adapted to provide an increasing mechanical advantage over the lever stroke because lever movement is necessary before the lever reaches the engagement point and thus, the start position of the lever must typically be at least 5 mm beyond the engagement point to accommodate this “dead-band.” With the Brand A lever, having the most favorable pivot spacing at 50 mm, this would require an initial lever reach of at least 55 mm, which would be uncomfortable for all users except those having the largest hands. Finally, many riders chose to have their engagement point much closer to the bar than 50 mm, on the order 30 or even 20 mm. Known levers having their pivot points 50 mm or greater from the clamp axis significantly rob braking power from such users.